1. Summary of the Prior Art:
The term "centrifugal piston expander" was first defined in prior U.S. Pat. No. 4,513,575 as comprising a rotating body upon which one or more cylinders are mounted for co-rotation. Each cylinder defines a fluid pressure chamber extending from a point remote from the axis of rotation of the rotating body to a point proximate to the axis of rotation. The longitudinal axis of the fluid pressure chamber may be linear or arcuate but, in any event, no substantial portion of the longitudinal axis is radially disposed with respect to the rotational axis. A free piston is mounted within the cylinder for sliding, sealable movements through the pressure chamber. When the piston reaches its outermost position in the pressure chamber, an inlet valve is actuated and a charge of pressured gas is introduced into the fluid pressure chamber which drives the piston radially inwardly toward the axis of rotation by expansion of the pressured gas. The reaction force of the gas on the outermost end of the cylinder produces a torque to assist in the rotation of the rotating body. The pistons are returned to their outermost positions primarily by centrifugal force acting on such pistons, hence, a starting motor is required to get the centrifugal piston expander engine up to a sufficient rotatable speed to ensure the return of the pistons to their outermost positions.
A variety of centrifugal piston expander engines are disclosed in the aforementioned patent and also in prior U.S. Pat. Nos. 4,420,945; 4,433,551 and 4,449,379, assigned to the assignee of this application. In U.S. Pat. No. 4,433,551 there is disclosed in FIG. 5, a schematic diagram of the necessary apparatus for effecting a continuous circulation of the pressured gas employed to drive the centrifugal piston expander including a heat exchanger receiving the cooled expanded gas for refrigeration or air cooling purposes.
Further experimentation with centrifugal piston expander engines has revealed that the output torque produced by any such engine utilizing a free piston which is centrifugally returned to its outermost position in a cooperating cylinder, is generally of a cyclical nature and may actually generate a negative torque (with respect to the desired direction of the output shaft) during a portion of each cycle. Such negative torque results in a serious fluctuation in the speed of the rotary load driven unidirectionally by the power output shaft of the centrifugal piston expander engine. The reduction in such speed fluctuation is a primary object of the present invention.